Glass fibers have been used to reinforce various polymeric resins for many years. Some commonly used glass compositions for use in reinforcement applications include the “E-glass” and “D-glass” families of compositions. Another commonly used glass composition is commercially available from AGY (Aiken, S.C.) under the trade name “S-2 Glass.”
Glass fibers have been arranged to form fabrics for many years. In conventional glass fiber weaving operations, a glass fabric is woven by interweaving weft yarns (also referred to as “fill yarns”) into a plurality of warp yarns. Generally, this is accomplished by positioning the warp yarns in a generally parallel, planar array on a loom, and thereafter weaving the weft yarns into the warp yarns by passing the weft yarns over and under the warp yarns in a predetermined repetitive pattern. The pattern used will depend upon the desired fabric style.
Warp yarns are typically formed by attenuating a plurality of molten glass streams from a bushing or spinner. Thereafter, a coating (or primary sizing composition) is applied to the individual glass fibers and the fibers are gathered together to form a strand. The strands are subsequently processed into yarns by transferring the strands to a bobbin via a twist frame. During this transfer, the strands can be given a twist to aid in holding the bundle of fibers together. These twisted strands are then wound about the bobbin and the bobbins are used in the weaving processes.
Positioning of the warp yarns on the loom is typically done by way of a loom beam. A loom beam comprises a specified number of warp yarns (also referred to as “ends”) wound in an essentially parallel arrangement (also referred to as “warp sheet”) about a cylindrical core. Loom beam preparation typically requires combining multiple yarn packages, each package comprising a fraction of the number of ends required for the loom beam, into a single package or loom beam. For example and although not limiting herein, a 50 inch (127 cm) wide, 7781 style fabric which utilizes a DE75 yarn input typically require 2868 ends. However, conventional equipment for forming a loom beam does not allow for all of these ends to be transferred from bobbins to a single beam in one operation. Therefore, multiple beams comprising a fraction of the number of required ends, typically referred to as “section beams,” are produced and thereafter combined to form the loom beam. In a manner similar to a loom beam, a section beam typically includes a cylindrical core comprising a plurality of essentially parallel warp yarns wound thereabout. While it will be recognized by one skilled in the art that the section beam can comprise any number of warp yarns required to form the final loom beam, generally the number of ends contained on a section beam is limited by the capacity of the warping creel. For a 7781 style fabric, four section beams of 717 ends each of DE75 are typically provided and when combined offer the required 2868 ends for the warp sheet, as discussed above.
As previously discussed, a primary sizing composition is applied to the glass fibers, typically immediately after forming. Traditionally, the filaments forming the continuous glass fiber strands used in weaving fabric are treated with an aqueous starch-oil sizing, which typically includes partially or fully dextrinized starch or amylose, hydrogenated vegetable oil, a cationic wetting agent, emulsifying agent, and water, as is well known to those skilled in the art. For more information concerning such sizing compositions, see K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres, (3d Ed. 1993) at pages 237-244, which is specifically incorporated by reference herein. While such sizing compositions are generally robust enough to provide protection to the fibers during fiber forming and loom beam manufacturing processes, they normally are unable to protect the glass fibers, and in particular the warp yarn fibers, from abrasion and wear during high speed weaving. As a result, it is conventional practice in the textile weaving industry to pass the warp yarn through a slasher, which applies a slashing size to the warp yarns during the manufacture of the loom beam to provide the additional protection required, in a manner to be discussed later in more detail. More particularly, the slashing operation provides the vehicle to add additional film forming chemistry to the fibers forming the warp yarn sheet. Typically, the slashing size includes either fully or partially hydrolyzed polyvinyl alcohol (PVA) materials and is a mixture in the 6-8% solids range with a viscosity of 15 to 20 centipoise (CPS). The slashing size is typically applied by submerging the warp yarn sheet in a vessel containing the slashing size via a series of submersion rollers and then passing it through a squeeze roll system, which typically exerts 15 to 20 pounds per square inch of squeezing pressure on the coated yarn in addition to the dead weight of the squeeze roller (the squeeze pressure can vary due to yarn diameter), to remove the excess slashing size. The slashing size can be applied at an elevated temperature, e.g., in the range of 130 to 150° F. (54 to 66° C.) or at room temperature, depending upon the recommendations of the PVA producer. After squeezing the excess size from the yarn sheet, the slashing sized sheet is dried in any convenient manner known in the art, such as but not limited to passing the sheet over heated rollers and/or through a hot air drying oven. In a slasher incorporating heated rollers, or cans, the surface temperature of the cans is typically in the range of 240 to 280° F. (116 to 138° C.). The actual temperature profile of the drying cans depends in part on the can arrangement, number of cans, and yarn speed. In a hot air drying oven, the air temperature within the oven typically ranges from 275 to 300° F. (135 to 149° C.). After drying, the warp yarn sheet passes through a series of split rods to separate the warp sheets and through a hook reed assembly and comb to combine the warp sheets and assure that no ends are adhered to each other. The yarn sheet is then wound onto the loom beam.
Both the primary starch-oil coating and slashing size are not compatible with polymeric resin matrix materials used to impregnate woven fabric incorporating the coated yarns. As a result, these coatings must be removed from the fabric, e.g., by heat cleaning and/or scrubbing, prior to incorporation of a fabric woven from these yarns into the matrix material. For example, a typical one-step heat cleaning process can entail heating the fabric at 600 to 800° F. (316 to 427° C.) for 70-80 hours to remove the starch-oil primary sizing composition and slashing size. In an alternative two-step operation, the fabric is unrolled through an oven where it is exposed to a flame that burns off a portion of the sizes, and then heated at 600 to 800° F. (316 to 427° C.) for 50 to 60 hours. The first step of this two-step operation is sometimes referred to as caramelizing and is typically used to heat clean fabrics woven from coarse yarns, i.e., 7628 style fabric.
When a primary sizing composition that is compatible with the resin matrix material is applied to the individual glass fibers during forming, it has been found that the application of additional slashing size to protect the glass fibers is unnecessary. As a result, the need for additional fiber protection through the application of a slashing size is eliminated. However, it has been observed that when such warp yarns having a resin compatible coating are simply wound onto a loom beam from multiple section beams, for example by passing the warp yarn through a slasher without the addition of slashing size, heating, and drying (sometimes referred to as “dry slashing”) to form a loom beam, the number of loom beam defects, such as end breaks due to rolled and twisted ends, is excessive. Rolled ends, which is a condition wherein adjacent glass strands roll on top of each other and are twisted together, are particularly troublesome as they can lead to end breaks during weaving, which in turn are associated with fabric quality issues such as ends out, fuzzy ends, chaffed ends, and undesirable yarn splices.
Nevertheless, the capability to make loom beams with warp yarns having a resin compatible coating on a slasher without using slashing size is important since the main method of forming loom beams in the textile weaving industry is by use of a slasher, and most weaving operations already have this type of equipment.